1. Technical Field
This invention relates to multi-wall liners in general, and to cooled multi-wall liners in particular.
2. Background Information
In gas turbine engines and other internal combustion devices it is common to utilize multi-wall liners between two fluids, one at a substantially higher temperature than the other. The "hot" fluid, referred to hereafter as "core gas", passes by the inner wall of the liner and the "cool" fluid, referred to hereafter as the "cooling gas", passes by the outer wall of the liner. If the temperature difference between the core gas and the cooling gas is great enough, the liner may experience undesirable thermal stress and strain. To minimize or eliminate the stress and strain, it is known to cool the liner with the cooling gas. For example, cooling gas provided at a higher pressure than the core gas is bled through apertures within the outer and inner walls of the liner, subsequently joining the core gas flow. As the cooling gas passes through the liner, thermal energy is transferred from the inner wall to the cooling gas, thereby decreasing the difference in temperature between the inner and outer wall.
There are several shortcomings to cooling a multi-wall liner in this manner. If the core gas temperature is high enough and the cooling air is not uniformly distributed, the inner wall may experience thermal distortion and failure in those areas insufficiently cooled. Inner walls having insulative or heat reflective coatings are particularly sensitive to thermal distortion. Distortion can cause a coating to crack and disengage, and thereby expose an unprotected section to hot core gas flow ultimately resulting in failure. Nonuniform distribution of cooling air also increases the likelihood that high temperature core gas will enter and damage the liner. Core gas passing by the inner wall is normally at a lower average pressure than that of the cooling gas within the multi-wall liner. At discrete spots, however, poorly distributed cooling gas within the liner may be at a lower pressure than that of the core gas, resulting in hot core gas influx. The problem is exacerbated when the pressure of the core gas flow is nonuniform and contains high pressure peaks.
What is needed, therefore, is a multi-wall liner that can accommodate at least two fluids at significantly different temperatures, and one that facilitates the proper distribution of cooling gas therewithin.